1. Field of the invention
This invention relates to a sealed variable resistor, in particular, to that which is favorably usable in humid surroundings such as in bathroom and bathtub.
2. Description of the prior art
In electrotherapeutic devices directed to use in such a humid surrounding, it is the most important issue to assure water- and moistureproofings for variable resistors as output controller and power switches in the devices. Although perfect water- and moistureproofings are easily attainable for oscillators and batteries by only enclosing them in a waterproofed sealing container, it is very difficult to perfectly waterproof certain elements with movable parts such as variable resistor and power switch.
I earnestly studied various means which might solve this issue of prior art. As the result, I eventually devised a sealed variable resistor comprising enclosing a variable resistor and an arm member attached to a shaft of the variable resistor in a sealing container, and rotatably supporting a dial knob about a shaft outside the sealing container such that when said dial knob is energized, said arm member moves in association by virtue of magnetic force, as well as disclosing the sealed variable resistor in Japanese Utility Model Kokai No. 40,953/88.
This sealed variable resistor however has the disadvantage that it is low in reliability because a decreased adhesive strength between the arm member and dial knob results in undesirable slippage and backlash, as well as having the advantage that it easily realizes prescribed water- and moistureproofings and also a smooth operation. An attempt to improve the adhesive strength using stronger magnets however has proved insuccessful because this tends to cause a contrary effect, i.e. damaging the balance between the arm member and dial knob and leading to a low operability of the dial knob.